1. Field of the Invention
The invention relates to endoscopic instruments. More particularly, the invention relates to electrocautery probes for use with a resectoscope or hysteroscope and specifically relates to bipolar roller electrodes used in electrocautery probes.
2. State of the Art
Electrosurgical resection is a procedure in which damaged or enlarged tissue is excised with an electrocautery probe. Transurethral resection is an electrosurgical procedure in which a portion of the prostrate is excised by means of an instrument passed through the urethra. Endometrial ablation is an electrosurgical alternative procedure to hysterectomy for women with menorrhagia (abnormal or excessive uterine bleeding). In these procedures, the instrument typically used is called a resectoscope or hysteroscope. Prior art FIG. 1 shows a typical resectoscope 10 with an electrocautery probe 12. The resectoscope 10 includes a distal tube 14 and a proximal handle 16. A telescope 18 is located in the tube 14 and is provided with a proximal eye piece 20 for viewing the interior of the bladder or other operative site. The cautery probe 12 has a distal electrode 22 which is mounted between a pair of arms 23, 25. The arms 23, 25 are joined at their proximal ends to an electrode lead 27 which is coupled via the handle 16 to a wire 24 which is coupled to a source of cautery current (not shown). A mounting sleeve 29 is provided on the probe 12 for slideably coupling it to the tube 14. The mounting sleeve 29 is typically located at the point where the arms 23, 25 are joined to the electrode lead 27. The handle 16 is generally capable of axially sliding the probe 12 and its distally mounted electrode 22 relative to the tube 14.
The ablation or resection procedure involves applying a cauterizing voltage to the electrode 22 and moving the electrode slowly over the prostate or endometrium while viewing the tissue through the scope 18. Thermal energy is applied through the electrode to the prostate or the endometrium so that tissue is excised. The resectoscope and cautery probe are also useful in other procedures for resecting the uterus, ureter, or renal pelvis.
Known electrodes for use in resectoscopes are available in many different shapes and sizes. U.S. Pat. No. 4,917,082 to Grossi et al., for example, discloses several embodiments of a "Resectoscope Electrode" including a coagulating electrode, a knife electrode, a punctate electrode, and a roller electrode, among others. Electrodes for use with resectoscopes are also widely available from Olsen Electrosurgical, Inc., Concord, Calif. They are available as blades, needles, balls, loops, spear tips, flexible wires, semi-circular wires, hooks, spatulas and blunt tips.
Recently, the generally preferred electrode for use in endometrial ablation is the roller (often referred to as "roller bar" or "roller ball") electrode. Prior art FIG. 1 shows a roller bar electrode 22. The roller bar is approximately 2.5 mm long and has a central bore 22b. It is rotatably mounted between the arms 23, 25 at the distal end of the electrocautery probe 12 by means of an axle wire 21 which extends through the central bore 22b of the electrode 22. The roller bar is supplied with a cauterizing voltage through the wire 21 which is coupled to the arms 23, 25 in the probe 12. When energized, the electrode 22 is rolled across the endometrial surface methodically until desired areas of the endometrium have been ablated. Roller bar electrodes are also used in prostatic resection.
It is generally appreciated in the art of electrocautery that bipolar cautery is safer and more effective than monopolar cautery. Monopolar electrosurgical instruments employ the instrument as one electrode, with a large electrode plate beneath and in contact with the patient serving as the second electrode. High frequency voltage spikes are passed through the instrument to the electrode of the endoscopic instrument to cause an arcing between the instrument and the proximate tissue of the patient. The current thereby generated continues through the patient to the large electrode plate beneath the patient. Monopolar cautery has the disadvantage that the current flows completely through the patient. Because control of the current path through the body is not possible, damage can occur to tissue both near and at some distance from the surgical site. In addition, it is has been observed that monopolar cautery can result in excessive tissue damage due to the arcing between the endoscopic instrument and the tissue.
In order to overcome the problems associated with monopolar cautery instruments, certain bipolar endoscopic instruments have been introduced. In bipolar electrosurgical instruments, two electrodes which are closely spaced together are utilized to contact the tissue. Typically, these bipolar instruments have two end effectors, e.g. a pair of scissor blades or a pair of forceps. One end effector acts as the first electrode, and the other end effector acts as the second electrode, with the end effectors being electrically isolated from each other and each having a separate current path back through to the handle of the instrument. Thus, in a bipolar instrument, the current flow is from one end effector electrode, through the tissue to be cauterized, to the other end effector electrode.
The use of bipolar electrodes in conjunction with resectosopes is known. U.S. Pat. No. 4,060,087 to Hiltebrandt et al. describes a simple double cutting loop electrode wherein each tungsten loop is an electrode and current flows from one loop to the other. The loops are spaced apart from each other by approximately 0.3 to 3.0 millimeters depending on the frequency of the cautery current. However, the distance between the loops must be precisely fixed to ensure cutting and avoid unintended coagulation of tissue. U.S. Pat. No. 4,116,198 to Roos discloses a similar bipolar double loop electrode as well as a bipolar electrode having a single loop and an adjacent non-loop electrode. The non-loop electrode may take the form of a coaxial cylindrical or semi-cylindrical shield or a pair of planar members mounted on opposite arms of a loop electrode. Nevertheless, there is no presently known way to utilize bipolar cautery techniques with a roller electrode used in endometrial ablation or transurethral resection.